1. Field of the Invention
The present invention relates to a wireless communication system, and more particularly, to a method of transmitting and receiving data in a wireless communication system.
2. Discussion of the Related Art
Recently, standardization of an IEEE 802.16m system is in progress. However, IEEE 802.16e terminals of the related art have already come into wide use at a point of time when the IEEE 802.16m system is commercially available. Accordingly, the IEEE 802.16m system needs to be standardized to be compatible with the IEEE 802.16e system. The IEEE 802.16m system requires a frame structure capable of supporting an IEEE 802.16e terminal.
The frame of the IEEE 802.16m system includes a plurality of subframes. A subframe includes a plurality of subcarriers on a frequency axis and includes a plurality of OFDM symbols on a time axis. Some of the plurality of subframes included in one frame are used for transmitting uplink data and the rest are used for transmitting downlink data.
In order to support the IEEE 802.16e terminal, the IEEE 802.16m system uses some downlink subframes for the IEEE 802.16m system and uses the rest of the downlink subframes for the IEEE 802.16e system. A zone used for the IEEE 802.16e system is called a wireless metropolitan area network orthogonal frequency division multiple access downlink zone (hereinafter, referred to as “WirelessMAN OFDM DL zone”) and a zone used for the IEEE 802.16m system is called an Advanced Air Interface downlink zone (hereinafter, referred to as “Advanced Air Interface DL zone”).
A downlink frame structure with a bandwidth of 7 MHz of the IEEE 802.16m system according to the related art will be described with reference to FIGS. 1 and 2. FIGS. 1 and 2 show an example of the case where a ratio of downlink to uplink subframes is 4:2.
FIG. 1 is a diagram showing a downlink frame structure according to the related art in the case where a frame offset is 1, and FIG. 2 is a diagram showing a downlink frame structure according to the related art in the case where a frame offset is 2.
The frame offset according to the related art defines an offset between a start point of a frame for an IEEE 802.16e system and a start point of a frame for an IEEE 802.16m system in the unit of subframes. However, since the frame for the IEEE 802.16m system includes one or more downlink subframes, the frame offset is an integer equal to or greater than 1 and less than the number of downlink subframes. For example, if one frame includes four downlink subframes, the frame offset is an integer equal to or greater than 1 and less than 4.
The subframes for the IEEE 802.16m system may be divided into four types. A type 1 subframe includes six OFDM symbols, a type 2 subframe includes seven OFDM symbols, a type 3 subframe includes five OFDM symbols, and a type 4 subframe includes nine OFDM symbols.
As shown in FIGS. 1 and 2, in the frame structure of the related art, the WirelessMAN OFDMA DL zone includes a type 1 subframe. That is, the WirelessMAN OFDMA DL zone includes six OFDM symbols in FIG. 1 and the WirelessMAN OFDMA DL zone includes 11 OFDM symbols in FIG. 2. A preamble is allocated to a first OFDM symbol of the frame for the IEEE 802.16e system and a FCH and a DL-MAP are allocated to second and third OFDM symbols.
A subchannelization method of the IEEE 802.16e system includes partial usage of subchannel (hereinafter, referred to as “PUSC”), full usage of subchannel (hereinafter, referred to as “FUSC”) and adaptive modulation and coding (hereinafter, referred to as “AMC”). The PUSC includes two OFDM symbols, the FUSC includes one OFDM symbol, and the AMC includes three OFDM symbols. The second and third OFDM symbols, to which the FCH and the DL-MAP are allocated, are subchannelized by the PUSC.
Accordingly, referring to FIG. 1, odd OFDM symbols are present in a portion excluding portions, to which the preamble, the FCH and the DL-MAP are allocated, in the WirelessMAN OFDMA DL zone.
However, when the odd OFDM symbols are subchannelized, a FUSC or Band-AMC method should be used. Therefore, in order to report that the subchannelization method is changed, a control message should be transmitted to a terminal. If subchannelization is performed using the PUSC and subchannelization is then performed using another method, resources can not be consecutively used.
In addition, all subframes included in the Advanced Air Interface DL zone are type 2 subframes. However, since a superframe header (SFH) is composed of a type 1 subframe in an IEEE 802.16m system, it is preferable that the Advanced Air Interface DL zone includes a type 1 subframe.
As described above, in the frame structure of the related art, since the control message should be transmitted in order to inform the terminal that the subchannelization method is changed, overhead is increased. In addition, when the subchannelization is changed, resources can not be consecutively used. Thus, radio resources are wasted. Furthermore, the Advanced Air Interface DL zone does not include a type 1 subframe.